Why is KMnO4 Purple in Colour


Answer: In KMnO4, Mn is in +7 oxidation state and have all the 3d-orbitals vacant. Mn7+ ion is surrounded tetrahedrally by four oxide ions. All oxide ions have filled 2p-orbitals. There is transfer of an electron from filled 2p-orbitals of oxide ion to vacant d-orbitals of Mn7+ ion. Since p-orbitals are ungerade and d-orbitals are gerade, therefore, electron transition from p-orbitals of O2- to d-orbitals of Mn7+ ion is Laporte allowed i.e., ΔL = ±1 and also there is no change in spin multiplicity during electronic transition. Therefore, transfer of an electron is Laporte and Spin allowed. Therefore, KMnO4 is intensely purple in colour.

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